In a gas combustion engine a fuel is generally combusted with an oxidizer. Both the fuel and the oxidizer are provided to a combustion chamber where the combustion occurs. The combustion may either be caused by an ignition spark or some other means for igniting the mixture.
One system for providing the fuel and oxidizer to a combustion chamber involves providing a fuel inlet and an oxidizer inlet. In these cases, the fuel and oxidizer are provided through separate inlets or ports to the combustion chamber. The fuel inlet and the oxidizer inlet are generally oriented such that the flow of fuel and flow of oxidizer will interfere with one another to substantially intermix before combustion occurs.
In engines that include dense injector layouts or high outputs, the fuel inlet portion and the oxidizer inlet portion may be substantially coaxial. Therefore, the fuel and the oxidizer are provided along a substantially similar axis with an injector element. For example, concentric annuluses are formed where an inner annulus provides the oxidizer, while an outer annulus, substantially surrounding and coaxial with the first annulus, provides the fuel. As the oxidizer and fuel exit their respective ports, shear forces between the two flows are created and cause the fuel and oxidizer to substantially mix. After mixing, combustion occurs to produce the energy required.
One application for such a high output engine is a rocket engine. One example of a coaxial injector element for a rocket engine includes a central oxidizer post or tube, which forms the oxidizer inlet, fitted into a bore of a faceplate. An annulus is formed around the oxidizer tube and a fuel sleeve or face nut is placed into the bore to provide the dimensions of the fuel inlet. These systems are generally complex because they require an additional component to form the injector system. In addition, the face nuts and fuel sleeves are generally centered and aligned from the oxidizer post. Thus, the oxidizer post must be substantially fixed prior to the installation of the face nut or fuel sleeve. Moreover, the fuel sleeves add an additional complex machined component. In addition, the face nut cannot survive the demanding thermal environment in some systems. Further disadvantages of these two systems include that they are not easily scaled down for smaller or more compact injector systems and engines. Machining these components becomes significantly more complex and costly at smaller and smaller tolerances and sizes.
Another example of a coaxial injector provides centering elements on the oxidizer post itself. Features or tabs are included on the oxidizer post that engage features or detents on the face plate to insure a proper alignment and centering of the oxidizer post. This system generally results in high injector post costs, while also making it more difficult to place the tabs properly on the oxidizer post as the oxidizer post size is reduced. The tabs must be precisely placed on the post because they are the only alignment means of the post.
In a coaxial injector system, the flow rate of the fuel and the oxidizer are controlled by selecting appropriate annulus sizes and ratios of the fuel annulus size relative to the oxidizer annulus size. Moreover, precise placement of the oxidizer tube is desired so that the proper quantities of oxidizer and fuel are provided at the injection plane to allow a substantially complete and quick combustion. Therefore, it is desired to provide a system that allows for precise tolerancing of the injector flow features while decreasing the complexity and cost of the injector system. Also a system is desired that is substantially robust so that it remains in alignment during use in rigorous applications, such as in an application as a rocket engine.